The present invention relates to piston type compressors that convert the rotation of drive shafts to linear reciprocation of pistons by means of drive bodies such as swash plates.
A typical piston type compressor includes a crank chamber that is defined in a housing. A drive shaft is rotatably supported in the housing. Part of the housing is constituted by a cylinder block. A plurality of cylinder bores extend through the cylinder block. Each cylinder bore accommodates a piston. A swash plate is fitted to the drive shaft in the crank chamber and supported so as to rotate integrally with the drive shaft. A pair of shoes are provided for each piston to couple the piston with the peripheral portion of the swash plate. The swash plate converts the rotation of the drive shaft to linear reciprocation of the pistons. The reciprocation of the pistons compresses refrigerant gas.
Each pair of shoes holds the swash plate in between. Each shoe is received by a shoe seat in the associated piston. The shoes are slidable with respect to the swash plate and the associated pistons. Thus, each piston is rotatable about its axis in the associated cylinder bore. Rotation of the piston causes the piston to hit the swash plate. This produces vibrations and noise.
During operation of the compressor, a moment is applied to each piston. The moment acts in a lateral direction (a direction transverse to the axis of the piston). Rotation of the swash plate slides the shoes in the associated shoe seat of each piston. The sliding produces a lateral moment that tends to tilt the piston. Thus, part of the piston is strongly pressed against the wall of the associated cylinder bore. This obstructs smooth reciprocation of the piston and causes biased wear in the cylinder bore, especially at the location that is pressed by the piston. As a result, the seal between the piston and the cylinder bore becomes less effective over time.
Japanese Unexamined Patent Publication No. 8-61237 describes a compressor that solves this problem. In this compressor, a pair of arms project from the crank chamber end of each piston in a direction substantially perpendicular to the axis of the piston. A groove is defined in the distal end of each arm. A guide rod extends in the axial direction of the pistons between each pair of adjacent cylinder bores. Each guide rod is slidably held between a pair of adjacent arms extending from the associated pair of adjacent pistons. This structure restricts the rotation of each piston. Furthermore, lateral forces applied to each piston are transmitted through the arms and are received by the guide rods to prevent tilting of the piston.
However, the guide rods, which are employed to restrict rotation of the pistons, increase the number of components and assembly steps. This increases the production cost of the compressor. Japanese Unexamined Utility Model Publication No. 6-25573 describes a compressor that eliminates the need for such guide rods. In this compressor, bolts, which are used to fasten together housing elements, are extended between each adjacent pair of pistons to function as the guide rods. In this publication, it is only mentioned that the rotation of each piston is restricted by the engagement between the bolts and the arms of the piston. However, in the same manner as the previous publication, it is believed that the lateral moment applied to each piston is received by the bolt via the arms.
When inserting the bolts through the housing elements to assemble the housing, the thread at the distal ends of each bolt pass by the associated piston. Thus, the thread may contact and damage the piston. Damage to the piston affects the performance of the compressor. Furthermore, chips may be cut off when the piston is damaged by the bolt thread. If such chips remain in the housing, the chips may be caught between components and adversely affect the performance of the compressor.
Furthermore, when inserting each bolt through the housing elements, the bolt passes through the opposed grooves of adjacent piston arms. Thus, the bolt thread may damage the arm grooves. Damage to the arm grooves affects the dimensional accuracy at the engagement portion between the arm groove and the bolt. As a result, the rotation of the pistons in their cylinder bores and the lateral moment applied to each piston causes the bolts to be hit against the walls of the arm grooves. This produces noise.